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A 2x2x2 which allows only clockwise and counterclockwise turn alternatingly.
Oskar designed this puzzle after the Irreversible Cube which explains the similar stickers.
After presenting the predecessor Bram Cohen came up with a design challenge. This puzzle does not allow half turns. In the starting position only clockwise turns are allowed for each of the three dimensions. Afterwards only a counterclokwise turn is allowed for any of the three dimensions. Therefore in this puzzle all moves can be inverted unlike the Irreversible Cube.
There was the question whether this puzzle can be twisted in the solved state but with a counterclockwise move coming next. Bram Cohen answered this:
Turning a face is a 4-cycle, which is an odd permutation, ergo every move alternates the parity of the permutation. Since every move also flips which direction the next turn is in, the two of them are always correlated, so it's impossible to get back to what appears to be the start state but with the next type of move flipped.
In November 2013 (three months after the original) Oskar presented version 2 of the concept.
Brandon Enright presents a detailed analysis of this puzzle using GAP
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